A switchboard that has coped for years can reach its limit quickly after an EV charger, induction cooktop, new machinery or extra workstations are added. Knowing how to assess electrical load helps property owners and operators make informed decisions before nuisance tripping, overheating or costly disruption becomes the issue.
Electrical load assessment is not simply adding up every appliance rating and comparing the total with the main switch. A sound assessment considers how equipment is used, what operates at the same time, the capacity of the existing supply and the condition of the installation. For Melbourne homes, businesses and industrial sites, it is a practical first step when planning changes or investigating capacity concerns.
What electrical load means
Electrical load is the amount of electrical power being drawn by equipment connected to an installation. Lights, air conditioning, ovens, pumps, refrigeration, computers, motors and chargers all place a load on the supply when operating.
Equipment ratings are commonly shown in watts (W) or kilowatts (kW), while switchboards and circuit protection are generally rated in amps (A). On a typical single-phase 230 V supply, current can be estimated using this calculation:
Amps = watts ÷ volts
For example, a 2,300 W appliance on a 230 V circuit draws about 10 A. This is useful for understanding an individual appliance, but it does not determine the safe capacity of a whole property on its own. Three-phase systems, motor loads, power factor, starting current and diversity all need further consideration.
The key figure for a property is often maximum demand. This is the estimated highest load likely to occur under normal operating conditions, rather than the unlikely scenario where every connected item runs at full output at once.
How to assess electrical load: a practical process
A useful load assessment starts with accurate information about the supply, circuits and equipment. It should be treated as a planning and safety exercise, not a reason to alter wiring, protection devices or switchboard components without a licensed electrician.
Confirm the incoming supply and switchboard rating
First, identify whether the site has a single-phase or three-phase supply. Check the rating of the main switch, metering arrangement and any available documentation for the property. A residential property may have a relatively modest single-phase supply, while commercial and industrial premises often use three-phase supply to serve larger loads and distribute them more evenly.
The main switch rating is only one part of the picture. The capacity of the consumer mains, meter enclosure, switchboard busbars, circuit breakers, cabling and upstream network supply may each affect what can be added. An older switchboard can be particularly restrictive, even where the property appears to have sufficient supply capacity on paper.
Make an equipment schedule
List fixed and significant plug-in equipment, recording its rated power, voltage, phase and expected operating pattern. Product labels, manuals and nameplates are the best source. For commercial and industrial equipment, include model details and any manufacturer data for motor starting current or maximum input current.
At a home, the largest loads may include an electric oven, cooktop, ducted heating or cooling, electric hot water, pool equipment, EV charging and workshop tools. In a business, refrigeration, air conditioning, server equipment, kitchen appliances, lighting, pumps and machinery may be more relevant.
Small loads should not be ignored, particularly where they are numerous. A bank of computers, monitors, chargers and printers can become significant in an office, while several display fridges can materially change demand in a retail or hospitality setting.
Establish what runs at the same time
This is where load assessment becomes more realistic. An oven may cycle on and off, air conditioning may peak during hot weather, and an EV charger may operate overnight when other demand is low. Conversely, a commercial kitchen can have multiple high-load appliances operating together during service.
Consider the busiest credible operating period. For a home, this could be a winter evening with cooking, heating, hot water and vehicle charging occurring together. For a workshop, it may be a production run when extraction, compressors, machinery and lighting are all in use.
Diversity can reduce the calculated maximum demand because not every load operates continuously or concurrently. However, it must be applied carefully. Assuming diversity where the equipment genuinely does run together can lead to overloaded circuits and an undersized supply.
Check individual circuits, not only the main supply
A property may have enough overall capacity but still have overloaded branch circuits. A 10 A general power circuit, for example, cannot safely support several high-demand appliances simply because the main switch has spare capacity.
Review what is connected to each circuit and compare the likely load with the circuit breaker rating and cable capacity. Repeated tripping, warm power points, damaged outlets or extension leads being used as permanent solutions all warrant attention. Replacing a circuit breaker with a larger rating is not a safe fix unless the cable, connections and installation design have been assessed for it.
A simple example of a residential assessment
Consider a single-phase home with a 63 A main switch. The theoretical supply capacity is approximately 14.5 kW at 230 V, but that figure is not an automatic approval for new equipment.
The home has an 8 kW cooktop, 3.6 kW oven, 7 kW split-system air conditioning system, 3.6 kW electric hot water system and a proposed 7 kW EV charger. Adding the nameplate ratings gives more than 29 kW, well above the incoming supply capacity.
That does not necessarily mean every item must be removed or that the EV charger cannot be installed. Cooking appliances do not always draw their maximum rating, hot water may be controlled to run outside peak periods, and an EV charger may be configured for lower output or load management. The right outcome depends on actual use, existing demand and the available infrastructure.
A licensed electrician can assess the installation, calculate maximum demand in line with applicable requirements and determine whether load control, dedicated circuits, switchboard work or a supply upgrade is appropriate.
Commercial and industrial load assessment needs more detail
For business and industrial properties, load assessment should also consider operational continuity. A supply may technically support current demand but leave no practical headroom for planned expansion, seasonal peaks or critical equipment.
Three-phase load balance is particularly important. Unevenly distributed single-phase loads can place excessive demand on one phase, create voltage imbalance and affect equipment performance. A detailed assessment identifies which circuits sit on each phase and whether new loads can be allocated more effectively.
Motor-driven equipment requires extra care because motors can draw a high starting current. Compressors, pumps, extraction fans, hoists and machinery may create a short-duration demand that affects voltage stability and protective device selection. Variable speed drives, soft starters and modern electronic equipment can also influence power quality, so a simple nameplate calculation may not be enough.
Where a facility has interval data, monitoring or utility bills showing demand information, these records can provide a clearer view of actual peak use. They should be read alongside site operations, not in isolation. A quiet billing period may not represent the demand expected after a new tenant, expanded shift or equipment upgrade.
Signs your electrical load may need review
A formal assessment is sensible before major changes, but several warning signs justify arranging one sooner:
- Circuit breakers trip repeatedly when normal equipment is in use.
- Lights dim or flicker when motors, welders or large appliances start.
- The switchboard has little or no space for additional circuits.
- Power points, plugs, breakers or switchboard covers feel unusually warm.
- Extension leads and power boards have become permanent parts of the setup.
- New air conditioning, machinery, commercial equipment or EV charging is planned.
These signs do not always mean the incoming supply is inadequate. The cause may be a faulty appliance, poor connection, overloaded circuit, ageing switchboard or incorrectly distributed load. Prompt investigation helps identify the actual issue rather than masking it.
When an upgrade is the right answer
A load assessment may show that the best option is not a larger supply. Demand management, staged equipment operation, a lower-output charger or improved circuit distribution can sometimes achieve the required result with less disruption.
Where capacity is genuinely limited, the work may involve new dedicated circuits, switchboard upgrades, consumer mains upgrades, three-phase conversion or coordination with the electricity distributor. The scope depends on the property type, existing installation and future plans. For a commercial or industrial site, allowing headroom during planned works can be more cost-effective than revisiting the switchboard every time operations grow.
Electrical load is best assessed before equipment is ordered, not after it arrives on site. A qualified electrician can turn your intended use of the property into a practical, compliant electrical plan that supports what needs to run now and what may be added next.